The Preparation And Characterization Of Magnetic Nanocatalysts And Their Application In KnoevenagelCondensation

Magnetic nanomaterials possessing the unique physical and chemical properties have been widely applied in the fields of electronics, information, autocontrol, organic synthesis and biological medicine. Particularly, for the catalysis, Magnetic nanoparticles display excellent performance as the catalysts or catalyst supports. And the magnetic nanocatalysts can be easily separated with an external magnetic field. Thus they can resolve the difficulty of separation and recovery of the common nano-heterogeneous catalysts, which offers a novel way for the separation of the nanocatalysts. Knoevenagel condensation is one of the most common and versatile reactions for C=C bond formation. The condensation products are the extremely valuable intermediates occupying very important position in the field of chemical industry. Herein, extending the application of magnetic nanomaterials and making them be the efficient and green catalysts for the Knoevenagel condensation have great innovative and practical significance.The research was based on two main aspects. On one hand, Fe3O4@SiO2 magnetic nanocatalyst was prepared in two steps and characterized by some modern analysis and testing techniques (XRD, TEM, VSM, and FT-IR). The Knoevenagel condensation of benzaldehyde with malononitrile was chosen as a model reaction. The optimal reaction conditions were determined, improving the yield of product to 97.8%. Additionally, the comparison of different catalysts proved the SiO2 layer was the active component of Fe3O4@SiO2. Furthermore, the repeated reactions of benzaldehyde with malononitrile were carried out to attest the catalyst’s recyclability. The conversion and selectivity still reached 90.1% and 93.5% respectively at the seventh operation and there was no discriminable difference between the fresh catalyst and the spent one. In addition, the magnetic separation of the Fe3O4@SiO2 makes the catalyst possess the significant industrial application potential.11 diverse aldehydes were introduced to test the general applicability of Fe3O4@SiO2. We observed that most condensations proceeded smoothly. The existence of electron-withdrawing groups and benzene ring has positive effect on the condensations.On the other hand, MFe2O4 (M=Mn,Cu, Co,Zn and Ni) nanoparticles were prepared readily through solvothermal method and characterized by some modern analysis and testing techniques (XRD, TEM, VSM, FT-IR spectroscopy, ICP-MS, and the BET nitrogen adsorption/desorption technique). The Knoevenagel condensation of benzaldehyde with malononitrile was taken as probe reaction. All of the ferrites MFe2O4 demonstrated good catalytic performance, with Nano-NiFe2O4 exceeded all its counterparts. And the M element was determined as the key active component of the catalysts. Furthermore, the amount of NiFe2O4 was optimized to improve the yield of product to 97.8%. Additionally, the repeated reactions of benzaldehyde with malononitrile demonstrated that the NiFe2O4 owned remarkable recyclability and stability. Hence, the NiFe2O4 had huge advantage in industrial application. What’s more, the Knoevenagel condensations of diverse aldehydes with malononitrile or ethyl cyanoacetate indicated the general applicability of the NiFe2O4. The existence of electron-withdrawing groups and benzene ring in the aldehydes has positive effect on the condensations. And the activity of active methylene compounds showed a positive correlation with the electro negativity of electron-withdrawing groups on their ends.